Electromagnetic type fuel injector valve

ABSTRACT

An electromagnetic fuel injector of an internal combustion engine having a plurality of electromagnetic coils for valve driving wound separately on a bobbin in an axial direction. The bobbin has a step difference of the outer diameter so that the bobbin outer diameter in the region with the second coil to be wound thereon is smaller then the bobbin outer diameter in the region with the first coil to be wound thereon, and the bobbin inner diameter has a step difference in that the bobbin inner diameter in the region with the first coil to be wound thereon is made large partially so as to secure an annular space to interpose a seal ring therein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electromagnetic fuel injector for aninternal combustion engine.

2. Description of Related Art

In an electromagnetic fuel injection valve (sometimes called aninjection valve), opening and closing operation is performed bycontrolling an electromagnetic coil in energizing with current andinterrupting, and while the valve is opened, a fuel is injected to aintake air passage, a intake port or a combustion chamber.

As such an injector, a system is put to practical use, where in order toimprove rising characteristics while a valve is opened, high voltage isproduced by providing a drive circuit with a booster circuit, and whilethe high voltage is impressed to a coil of the injector, a currentcontrol circuit is used and a large current is forced to flow at a shorttime (for example, JP-A 6-241137). In the system, a battery voltage (forexample, 12V) is raised (for example, 70V) during the valve opening.Particularly, as, an applied injector, there is an injector inintracylinder injection system where a fuel pressure is high and a loadin a return spring is large (an injector where a fuel is injecteddirectly into a combustion chamber of a gasoline engine).

In an injector using a booster circuit, when a valve is opened asalready described, while a large voltage is impressed to anelectromagnetic coil, a large current flows in the coil.

After the valve is opened, since a fuel pressure within the injectordecreases and a return spring is not in the state of set load, force forholding the opened valve does not require magnetomotive force incomparison with the case of opening the valve. Accordingly while theopened valve is held, the voltage to the coil is changed from thebooster circuit into the battery voltage, and in the coil a relativelysmall current enough to hold the opened valve is flowed by using acurrent control circuit.

Further in recent years, technology is proposed where a booster circuitis not used and rising characteristics during the valve opening areimproved by a system impressing a battery (for example, JP-A 11-148439).In this system, two types of electromagnetic coils different in wirediameter and the number of turns of the coils are prepared. Among these,the first coil is mainly used during the rising operation while thevalve is opened (the operation that the valve moves from the closedposition to the fully opened position), and as characteristics, timevariation rate of the magnetomotive force is made large. Therefore inthe first coil, the wire diameter is made relatively large (the coilresistance is made small), and the number of turns is made small and alarge current flows in the coil with good response. Also since thecurrent is made large, the magnetomotive force is raised.

The second coil is mainly used to hold the state after the valve isopened. Accordingly the response property as in the case of the firstcoil is not required, and the large magnetomotive force as in the caseof opening the valve is not required. The time variation rate of themagnetomotive force may be small. Accordingly in the second coil, thewire diameter is made relatively small (the coil resistance is madelarge) and the number of turns is made large, and the magnetomotiveforce capable of holding the opened valve even at a small current isobtained.

In the battery voltage drive system, a booster circuit and a currentcontrol circuit as above described are not required. Accordingly thesystem is advantageous in that the cost reduction can be intended.

As above described, in the electromagnetic fuel injector valve, in orderto raise the output characteristics and the response property, proposalsare made and that the coil impressed voltage is raised and the coilcurrent is made large, or two types of the electromagnetic coilsdifferent in the characteristics are used. With accompanying this, thecountermeasure for heat generated in the coil is further required.Particularly an intense heat of the coil under the violent state of thehigh temperature circumstances such as the inside of the engine roomdeteriorates the state of the insulation film and the bobbin of the coiland results in the reduction of the life. Accordingly the countermeasurefor the intense heat generated in the coil is necessary.

Besides the countermeasure for the intense heat, when the first coil andthe second coil different in the characteristics are prepared as abovedescribed, the number of the coil terminals increases. Therefore theproblems remain in that how these terminals and other parts are madeintensive and rationalized and the injector is realized at compactstructure and low cost.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an injector in whichthese problems are solved and the heat radiation property of the coil ofthe injector accompanied by the performance improvement is raised, andwhich can entirely withstand the environment of the intense heat andassures its long life and moreover can intend to achieve the compactstructure and the cost reduction.

In order to attain the foregoing object, the present invention isbasically constituted as follows.

One is an injector with an electromagnetic coil for driving a valve,considering the heat radiation performance of the coil, where a bobbinfor winding the coil thereon is constituted by a synthetic resincontaining a filler having good heat conductivity.

Another is an injector where an electromagnetic coil for driving a valveis provided with two types of coils different in the characteristics,and these coils are wound separately in the axial direction of onebobbin, and among these coils, the winding region of one coil (the firstcoil) is near a movable core with a valve element being the object ofthe magnetic suction and the winding region of the other coil (thesecond coil) is away from the movable coil, and where the bobbin has astep difference of the outer diameter so that the bobbin outer diameterin the region with the second coil to be wound thereon is smaller thanthe bobbin outer diameter in the region with the first coil to be woundthereon, and on the other hand, the bobbin inner diameter in the regionwith the first coil to be wound thereon is partially enlarged and thestep difference of the inner diameter is formed so that the annularspace to interpose the seal ring is secured.

Another is an injector having a first coil and a second coil differentin characteristics as above described in order to intend simplificationand rationalization of parts, where a connector part comprising threeterminals is provided, and the above-mentioned first and second coilsare connected to the power source and two switching elements forenergizing control through the three terminals.

In order that electromagnetic coil relevant parts are made intensive andcompact, another injector is constituted as follows.

That is, in an electromagnetic fuel injector where a first coil and asecond coil as above described are arranged in the axial direction ofone bobbin, and a connector part to connect terminals of these coils toan external power source and a switching elements is provided to projectlaterally at the upper side of the bobbin as above described,

characterized in that plural terminals of said first and second coilsare arranged on the upper end surface of said bobbin, and at least oneof these terminals has the base part positioned at the opposite side ofthe connector part with respect to the axial line of the main body ofthe injector, and this terminal has a curved part formed at the midwayled from the base part to the connector part so as to avoid the axialline.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1(a) is a longitudinal sectional view of an injector according toan embodiment of the invention, and

(b) is a front view of a connector part of the injector;

FIG. 2 is a perspective view of the injector;

FIG. 3 is an exploded perspective view of the injector;

FIG. 4 is a front view showing an electromagnetic coil module to be usedin the injector;

FIG. 5 is a drive circuit constitution diagram of an electromagneticcoil in the embodiment;

FIG. 6 is an explanation diagram showing a state that a valve openingsignal is sent from an engine control unit to an injector;

FIG. 7 is a time chart showing coil energizing control of an injector inthe embodiment;

FIG. 8 is a six-face view showing an example of a coil terminal to beused in the embodiment;

FIG. 9 is a diagram showing a coil connection mode in another embodimentof the invention: and

FIG. 10 is a fragmentary exploded perspective view of a coil module inanother embodiment of the invention.

DESCRIPTION OF THE PREFFRRED EMBODIMENTS

An embodiment of the present invention will be described based on thedrawings.

At first, the structure of an injector 10 in the embodiment will bedescribed using FIG. 1.

The injector 10 is constituted by a stationary core 11, electromagneticcoils 12, 13, a yoke 14, a movable unit (also referred to as a movablecore, a plunger or the like) 19 having a valve element 21, a nozzle 22,a return spring 26, an external resin mold 34 with a connector 34 a andthe like.

The movable unit 19 in this embodiment comprises a cylindrical movablecore 19′ having magnetism and a valve rod 20 coupled integrally.

In the inside of the cylindrical yoke 14 being a body of the injector,the stationary core (center core) 11, and the first coil 12 and thesecond coil 13 wound on a bobbin 15 are arranged from the centerposition toward the outside. The structure of the bobbin 15 and detailsof the coils 12, 13 will be described later.

The stationary core 11 is formed in a slender hollow cylinder, and thehollow part is a fuel passage 33. A part of the core 11 is positioned atthe center within the yoke 14, and the other part is projected upwardfrom the yoke 14. At the outer circumferential part of the core 11, aflange 11 a is molded integral with the core 11. In the flange 11 a,terminal holes 40 are arranged so that a plurality of coil terminals35-37 provided on the bobbin 15 are inserted therethrough. The flange 11a is fitted to the upper opening of the yoke 14, and presses the innercircumferential edge of the yoke 14 locally and produces a metal flow(plastic flow). Thus the flange 11 a is tightly coupled with the yoke14. Numeral 14 a in FIG. 1 designates trace of the metal flow.

The movable unit 19 is coupled integral with the spherical valve element21, and is arranged in line with the core 11 in the axial direction. Thereturn spring 26 is located between a spring adjuster 41 fixed withinthe hollow cylinder of the core 11 and a spring shoe within the movableunit 19, and applies a spring load in the valve opening direction to themovable unit 19. By the spring load, when the electromagnetic coils 12,13 are not energized with a current, the valve element 21 is pushed to asheet 22 a provided at the nozzle 22 and closes an injection port 25.

When the electromagnetic coil is energized with current, a magnetic pathis formed by the yoke 14, the stationary core 11 and the movable core19′, and the movable unit 19 is subjected to the magnetic suction towardthe side of the core 11 and the valve element 21 is separated from theseat 22 a and becomes the valve opened state. The stroke in the valveopening direction is restricted in that a part of the movable unit 19(for example, the valve rod 20) abuts on a stopper 27.

During the valve opening, a pressurized fuel passes through a filter 32,a passage 33 and a passage 33′ provided at the side of the movable unitand passes from the inside of the nozzle 22 through a groove 24 a formedalong from the side to the bottom in a swirler (a fuel swirling element)24, and then it is swirled and injected from the groove between thevalve element 21 and the seat 22 a. The output side of the groove 24 ais opened to the inner circumferential surface of the swirler 24 so asto be shifted to the tangential direction with respect to the swirlercenter axis. Thus the fuel swirls and flows out from the groove 24 a tothe swirler center hole.

As an example of the injector according to the embodiment, that ofdirect injection system is exemplified where the injection port 25 facesthe inside of the cylinder (combustion chamber) of the internalcombustion engine and the high pressure fuel is injected directly intothe cylinder. The electromagnetic coil is constituted by a first coil(referred to as “valve opening coil” here) 12 to be used mainly duringthe valve opening so as to raise the valve element 21 from the seatposition to the predetermined opening stroke position (the openingstroke is restricted by the stopper 27, and the opening stroke operationis referred to as “valve opening operation”), and a second coil(referred to as “holding coil” here) 13 to be used to hold thesubsequent valve opening state.

In the direct injection system, since the injector is opened and closedin the combustion chamber, during the valve closing, the valve must bemade not opened by the pressure during the explosion process. Alsoduring the valve closing, the fuel must be injected into thehigh-pressure atmosphere in the compression process. Accordingly, incomparison with the system that the fuel is injected to the suctionpassage, the large return spring set load and the high fuel pressure arerequired. During the valve opening operation, the rising characteristicsare required in that the magnetic suction force (magnetomotive force) toexceed the fuel pressure and the set load is generated with goodresponse.

In order to obtain such rising characteristics during the valve opening,there are two systems as follows. One is a system that a large voltage(for example, about 70V) is impressed to an electromagnetic coil using abooster circuit, and a large current (for example, about 8 A) is letflow in the coil using a current control circuit in a short time.Another is a system that a booster circuit and a current control circuitare not used, but the number of turns is made relatively little and wirediameter of a coil is made large (coil resistance is made small) and abattery voltage is impressed to the coil directly. Therefore a largecurrent is let flow in the coil in a short time.

In this embodiment, the latter system (so-called battery voltageimpressing system) is adopted. The coil with the coil wire diameterbeing large and the number of turns being relatively little correspondsto the valve opening unit 12. The time variation rate of themagnetomotive force is large. The specific mode of the coil wirediameter, the number of turns or the like will be described later.

When the opened valve is to be held, since the fuel is already injected,the fuel pressure is decreased and the air gap between the movable unit19 and the core 11 becomes small. Accordingly in the operation ofholding the opened valve, the movable unit 19 can be held to the openstate in smaller magnetomotive force than that during the valve openingoperation.

In the opening valve holding state, in the system of the embodiment(battery voltage impressing system), the holding coil 13 having the coilwire diameter less than that of the valve opening coil 12 (coil 13 islarge resistance) and the number of turns being relatively much isimpressed by the battery voltage (in this case, the holding coil 12 andthe valve opening coil 13 may be connected in series and both coils maybe energized with current, and in the embodiment, such manner is done asdescribed later). Thus the current flowing in the electromagnetic coilis decreased to the valve enough for the magnetomotive force to hold theopened valve (for example, about 3 A). In addition, in the system usingthe booster circuit as above described, in the opened valve holdingstate, the coil impressed voltage is changed to the battery voltage andthe coil current is made small using the current control circuit.

Hereupon, the connection structure of the valve opening coil 12 and theholding coil 13 and relation to the coil drive circuit as abovedescribed by FIGS. 5 and 6.

In the embodiment, basically, a connector part 34 a comprising threeterminals (a first terminal 36, a second terminal 35, a third terminal37) is provided as shown in FIG. 1 and FIGS. 3 to 5. By the threeterminals, the valve opening coil (first coil) 12 and the holding coil(second coil) 13 are connected to a battery power source 53 and twoswitching elements 51 a, 51 b for energizing control as shown in FIG. 5.

The terminal 36 connects one end of the valve opening coil 12 to theplus side of the battery power source 53, and the terminal 35 connectsthe other end of the valve opening coil 12 to a switching element 51 afor valve opening and also to one end of the holding coil 13, and theterminal 37 connects the other end of the holding coil 13 to theswitching element 52 a for the opened valve holding.

In the above-mentioned constitution, the terminal 35 is the terminal toconnect the valve opening coil 12 to the switching element 51 a, andalso serves as an intermediate terminal to connect the valve openingcoil 12 and the holding coil 13 in series connection state (when theswitching element 51 a is turned off and the switching element 52 b isturned on the coils 12 and 13 become series connection state).Accordingly terminals of two types of coils different in thecharacteristics need not be made four terminals in total, and thereduction of the number of parts can be intended.

In addition, in the embodiment, one end (minus side) of the holding coil13 is connected through a diode 50 to the switching element 52 a.

These coils 12, 13 are in the same direction in the wire windingdirection, and both coils are added to each other in the magnetomtiveforce for a current flowing in the same direction. In the switchingelements 51 a, 52 a, for example, a semiconductor switching element suchas a power transistor may be used.

The drive circuits 51, 52 are constituted by transistor module providedwith the switching elements 51 a, 52 a and the surge absorbing diodes 51b, 52 b respectively.

The switching element 51 a becomes a switching control element of thevalve opening coil 12, and its collector is connected to the terminal35, and its emitter is connected to the ground 54 of the battery powersource 53. Its base inputs a control signal from the engine control unit(hereinafter referred to as “ECU”) 55 (refer to FIGS. 5 and 6).

The switching element 52 a mainly becomes an energizing control elementof the holding coil 13, and its collector is connected through the diode50 for reverse current inhibiting to the terminal 37, and its emitter isconnected to the ground 54 of the battery power source 53. The diode 50for reverse current inhibiting may be provided between the drive circuit52 and the ground 54. Its base inputs a control signal from the ECU 55.

Here, a specific example of energizing control of the coils 12, 13 willbe explained with reference to FIG. 5 and FIG. 7.

FIG. 7 is a time chart during the valve opening operation of theinjector 100, and shows wave forms of an injection command signal, aswitching element for a valve opening coil, a switching element for aholding coil, a valve opening coil current and a holding coil current.

If the injection command signal in response to a state of the engine isoperated by the ECU 55, the switching element 52 a is ON-controlled onlyin the same time Ti as the injection command signal. On the other hand,the switching element 5 a is ON-controlled only in the short time Tcfrom the output start of the injection command signal. Accordingly,during the time Tc, any of the valve opening coil 12 and the holdingcoil 13 becomes an energizing state. However, the coil resistance islarger in the coil 13 than in the side of the coil 12. Therefore thealmost current flows from the valve opening coil 12 to the side of theswitching element 51 a.

In the valve opening coil 12, since the coil resistance and theinductance are small, a large current flows rapidly. Therefore themagnetomotive force necessary for the valve opening operation isgenerated with good response. That is, the valve opening coil 12 hascharacteristics that the time variation rate (rise) of the magnetomotiveforce is large. The energizing time for the current to flow in the coil12 is limited to a short time until the valve opening operation, andmoreover the number of turns is little. Thus the heating can besuppressed.

During the time Tc, the mutual induction phenomenon by the mutualinductance is produced between the valve opening coil 12 and the holdingcoil 13. Thus when the valve opening coil 12 rises largely, theelectromotive force in the reverse direction is generated in the holdingcoil 13.

When such electromotive force is generated, if there is no diode 50, itfollows that the reverse current as shown by broken line in FIG. 7 flowsfrom the side of the ground 54 through the surge absorbing diode 52 b inthe holding coil 13. The reverse current produces a magnetic flux in theholding coil 13. However, the magnetic flux is produced in the directionthat a magnetic flux generated in the valve opening coil 12 isdecreased. If the reverse current is allowed, the produced magnetomotiveforce substantially during the valve opening will be decreased. In orderto avoid this, as shown in FIG. 5, the diode 50 for reverse currentpreventing is provided between the terminal 37 and the ground 54.

After the time Tc (after the valve opening), the switching element 51 ais turned off and the switching element 52 a continues the ON-state.Thus the valve opening coil 12 and the holding coil 13 are connected inseries. Therefore the same current flows in the coils 12, 13. Thecurrent value becomes the value that the battery voltage is divided bythe sum of the resistance values in the coils 12, 13. The number ofturns and the resistance of the holding coil 13 arte further larger thanthat of the valve opening coil 12. Thus the coil current is determinedsubstantially by the resistance of the holding coil 13. In the time fromTc to Ti, current flows in the holding coil 13 having the number ofturns relatively much and the magnetomotive force becomes large, andcurrent flows also in the valve opening coil 12 having the number ofturns relatively little. In such constitution, in comparison with thecase that a current flows in the holding coil 13 only, the largemagnetomotive force can be obtained in total. In addition, such coilconstitution and energizing control can be realized in the directinjection system without using the booster circuit and the currentcontrol circuit. Thus such constitution is advantageous in the cost, andalso has the high speed response property. Therefore the presentapplicants already propose such constitution as the prior patentapplication (JP-A 11-100972).

In order to provide the above-mentioned characteristics, in theembodiment, the wire diameter of the valve opening coil 12 is maderelatively large, for example, about φ0.45-φ0.65 mm, and the number ofturns is made 40 turns, and the inner resistance is made about 0.13 Ω.Also the wire diameter of the holding coil 13 is made, for example,about φ0.15 mm, and the number of turns is made 135 turns, and the innerresistance is made about 5.5 Ω.

The coils 12, 13 are arranged separately in the axial direction on onebobbin 15 as shown in FIG. 1, and the valve opening coil 12 is near themovable unit 19 in comparison with the holding coil 13. In suchconstitution, during the valve opening operation, magnetic flux producedin the coil 12 can pass through the movable core 19′ and the stationarycore 11 with a little loss, and the rising characteristics of the valveopening operation become better.

When the current flowing in the electromagnetic coil becomes large asabove described, amount of heat generated increases. Therefore the heatradiation measure becomes necessary. Accordingly, the bobbin 15 isconstituted by a synthetic resin containing a filler having good heatconductivity.

In the embodiment, as a synthetic resin material of the bobbin 15, PPSexcellent in the heat resisting property is adopted, and iron oxide as afiller having good heat conductivity is contained in the PPS. Forexample, the PPS is in 60 and several weight %-10 and several weight %,and the iron oxide is in 30-80 weight %, and a glass fiber is in severalweight %-10 and several weight %. Regarding the PPS, any of bridgingtype or straight chain type may be used. In the case of straight chaintype, it is excellent in impact resisting property and welding strength.The PPS has the heat conductivity being 0.4 W/mk, and PA (polyacetal)resin in 6-nylon series widely used in such a bobbin in the prior arthas the heat conductivity being about 0.2-0.3 W/mk. Accordingly the PPSresin has the good heat conductivity of the resin material itself incomparison with the bobbin resin in the prior art. When the iron oxidein 30 weight % is contained in the PPS resin, the heat conductivitybecomes 1 W/mk. Also when the iron oxide in 80 weight % is contained inthe PPS resin, the heat conductivity becomes 3 W/mk. However, if thefiller is contained in 80 weight % or more, a difficulty is produced inthe molding. Thus the upper limit of the filler content is preferablyless than this value.

The present inventors have made an article on an experimental basis andperformed the estimation test of the article in the case that normalworking in twenty years was supposed and the upper limit value of theheat resisting temperature of the coil film was made 242° C.

An example of the test results is shown Table 1 below.

TABLE 1 Specification Temperature Holding coil Valve opening coilBetween rise (° C.) Wire Re- Wire Re- core (Duty 40%) dia- sis- dia-sis- Bobbin and No With No. meter Turns tance meter Turns tance materialbobbin fuel fuel 1 φ 90 4.0 φ 40 0.13 PPS Contact 238.5 — 0.15 Ω 0.65 Ω0.4 w/mk 2 φ 90 3.7 φ 40 0.13 PPS + Pad 100.7 85.9 0.15 Ω 0.65 Ω goodheat conducting filler 3 w/mk 3 φ 90 3.7 φ 40 0.13 PPS + Conduc- 132.5124.6 0.15 Ω 0.65 Ω good heat tive conducting adhe- filler sive 1 w/mk 4φ 180 7.7 φ 40 0.13 PPS + Contact 44.9 39.1 0.15 Ω 0.65 Ω good heatconducting filler 3 w/mk 5 φ 180 7.7 φ 40 0.13 PPS + Conduc- 80.4 68.20.15 Ω 0.65 Ω good heat tive conducting adhe- filler sive 1 w/mk 6 φ 1807.7 φ 40 0.13 PPS + Contact 106.0 97.2 0.15 Ω 0.65 Ω good heatconducting filler 1 w/mk 7 φ 135 5.5 φ 40 0.13 PPS + Contact 127.2 127.20.15 Ω 0.65 Ω good heat conducting filler 1 w/mk 8 φ 90 3.7 φ 30 0.09PPS + Contact 128.9 128.9 0.15 Ω 0.65 Ω good heat conducting filler 3w/mk

In the experiment, the duty of the injection driving was made 40percent, and the injector was driven under the environment temperaturebeing the normal temperature (20° C.), and the coil temperature wasmeasured. In the table, the area between the core and the bobbin meansmode between the outer circumference of the stationary core 11 and theinner circumference of the bobbin 15, and the “contact” means the casethat both the core 11 and the bobbin 15 are contacted in the closecontact state, and the “conductive adhesive” means that both as abovedescribed are adhered with the adhesive having the heat conductivity,and the “pad” means that the heat conductive material is filled betweenboth as above described.

Also item “temperature rise” in the table is divided into “no fuel” and“with fuel”. The “no fuel” means that assuming the gasification of thefuel within stationary core 11, the injector is driven in the state ofno fuel and the temperature rise of the coil is measured. The state thatthe fuel within core 11 is gasified, means the case that when the insideof the engine room is at the high temperature environment of, forexample, about 130° C. (when the temperature is high as in themidsummer, the high load working performed continuously, and thenimmediately after the engine is stopped, such high temperature state isproduced) and also the injector is at the stop state, such gasifiedstate is produced.

The “with fuel” means the case that the fuel is in the liquefied statewithin the stationary core 11. The injector according to No. 1 means aninjector according to the comparative example where a glass fiber iscontained in the PPS resin as a bobbin. In the injector according to No.2 or later, the filler of good heat conductivity (iron oxide, here) iscontained in the PPS resin as a bobbin (however, a glass fiber filler iscontained in several weight % ten and several weight %). Among them, theheat conductivity being 3 W/mk is the case that the containing ratio ofthe filler of good heat conductivity is 80 weight %, and the heatconductivity being 1 W/mk is the case that the containing ratio of thefiller of good heat conductivity is about 30 weight %.

As a result of the endurance test, in the case of No. 1, in theenvironment of the normal temperature (20° C.) and “no fuel”, the coiltemperature rises to 238.5° C. In the case that the inside of the engineroom is at the high temperature environment (130° C.), it is supposedthat the coil temperature is further rises by 110° C. (130° C.−20° C.).Accordingly when the inside of the engine room is at the violent hightemperature environment, the coil temperature becomes (238.5° C.+110°C.), and this entirely exceeds the heat resisting temperature 242° C. ofthe coil film.

On the contrary, in the case of the injector at No. 2 or later, the heatradiation characteristics of the coil temperature is improved by thebobbin. Therefore the coil temperature remains about 132.5° C. at most,even in the case of “no fuel” at the environment of the normaltemperature. Accordingly even if the inside of the engine room is at theviolent high temperature environment, the coil temperature is about(132.5° C.+110° C.). Except for the case of No. 3, the result isobtained that the coil temperature is less than the coil film resistingtemperature 242° C. The heating of the coil in this case is radiatedfrom the bobbin 15 through the core 11 and the yoke 14.

Among them, considering the molding property of the bobbin, the coilresistance and the aspect of the cost, that of No. 7 is at good balancesynthetically. Therefore according to the embodiment, even if the coilheating temperature rises by the coil exciting current being largeaccompanied by the improvement of the performance of the injector, theexcellent heat radiation performance can be exhibited and the long lifeof the injector can be secured.

In addition, in place of the direct injection system (DI system), in theinjection in the system that a fuel is injected at the suction passage,the coil current does not become larger as in the DI system. Thereforein the case, even at the injection specification of No. 1 (the heatconductivity of the bobbin being 0.4 W/mk) in the above-mentioned table,the heat radiation performance can be raised in comparison with theinjector of similar type until now.

Further in the embodiment, in addition to the heat radiating property ofthe coil, the bobbin structure is adopted where parts can be arranged atintensive method rationally.

Regarding the bobbin 15, as shown in FIG. 1, the step difference of theouter diameter is provided so that the bobbin outer diameter in theregion with the holding coil 13 wound thereon is smaller than the bobbinouter diameter in the region with the valve opening coil 12 woundthereon. On the other hand, the bobbin inner diameter in the region withthe valve opening coil 12 wound thereon has the step difference of theinner diameter 153 where a part of the inner diameter becomes large, inorder to secure the annular space S for the interposing of the seal ring18 of the non-magnetic property.

In such constitution, the seal ring 18 can be installed between theouter circumference at the top end of the stationary core 11 and theinner bottom of the yoke 14 in the state that the bobbin inner space Sis utilized effectively. Moreover the bobbin is thinned at the positionwith the seal ring 18 existing and at the position with the holding coil13 existing and thereby the heat of the electromagnetic coils 12, 13 canbe escaped to the side of the core 11 efficiently (a part of the heatcan be escaped through the seal ring 18 to the core 11 and the yoke 14).

Particularly when the heat of the coils 12, 13 is conducted through thebobbin 15 having good heat conductivity to the core 11 and the yoke 14as in the embodiment, even if a gap between the most outside in the coiland the yoke 14 remains as it is, the sufficient heat radiation of thecoil is assured. Also since the gap remains as it is, the cost reductionis intended, and moreover the gap can be utilized as the insulation gaplayer between the coil and the yoke.

In addition, in the seal ring 18, one end side (upper part side) iscoupled by the metal flow, and the lower end side is in edge shape andis cut into the yoke bottom part.

Thus it seals between the coil 11 and the yoke 14.

According to the bobbin structure, the injector is excellent in the heatradiating property of the coils 12, 13, and moreover the electromagneticcoil part and the seal part are made intensive and the injector is madecompact.

Next, the arrangement structure of the coil terminal will be explained.

In the coil terminal of the embodiment, the three-terminal structure isadopted as already described. Any of the three terminals is arranged atthe upper end surface of the bobbin 15. In coil terminals of theembodiment, three-terminal-structure is adopted as already described.Any of the three terminals is arranged on the upper end surface of thebobbin 15. Among them, the terminals 36, 37 are arranged on the axialline o of the main body of the injector, in other words, on the positionnear the connector part 34 a with respect to the core 11. The terminal35 is arranged in that the base part 35 a is on the opposite position tothe connector part 34 a. The terminal 35 is hidden in the shadow of thecore 11 viewing from the side of the connector part 34 a. Accordinglywhen the terminal 35 is to be led to the side of the connector part 34 astraightforward, the core 11 obstructs its path. Therefore in theembodiment, regarding the terminal 35, a curved part 35′ is formed fromthe base part 35 a at the midway led to the connector part 34 a, so asto avoid the axial line hence the core 11.

In the embodiment, considering the workability of the terminal 35, theterminal 35 is divided into a base part 35 a and a lead frame 35 b, andthe lead frame 35 b is welded to the base part 35 a. In any of theterminals 35, 36, 37, one end becomes a connector terminal.

In such constitution, when a plurality of coil terminals are arranged onthe bobbin end surface, the degree of freedom is raised, and moreover,three or more connector terminals (coil terminals) can be arranged onone connector in intensive method, and the injector is made compact.

The connector part 34 a is molded integrally with the mold resin 34constituting the upper external part of the injector. Viewing from thebobbin 15, the connector part 34 a is projected to the lateral side ofthe mold resin at the upper side. In the terminals 35-37, a part exceptfor the top end becoming the connector terminal is insert molded(embedded) in the mold resin 34.

Hereupon, the coil module to be used in the injector of the embodimentwill be explained using FIG. 4 and FIG. 8.

FIGS. 8(a)-(e) show a top view, a front view, a left side view, a rightside view and a bottom view of the base part 35 a in the coil terminal35. The base part 35 is formed integrally by a center pin 350 and armparts 351, 352 stretched laterally at the lower part of the center pin350, and is molded by the press working of a metal sheet. In the armpart 351, a part 351 a binding the winding finishing end 12′ of thevalve opening coil 12 is provided (refer to FIG. 4), and in an arm part352, a part 352 a binding the winding start end 13′ of the holding coil13 is provided. The coil end being bound is grasped by the binding parts351 a, 352 a and bending pieces 351′, 352′, and is joined in fusing withthe bending piece.

Series connection of the valve opening coil 12 and the holding coil 13becomes possible through the binding parts 351 a and 352 a, andconnection to the switching element 51 a for the value opening coil 12as already described becomes possible.

In the base part 35 a, a part is coated with an insulation resin mold asshown in an imaginary line (dash-and-dot line) 360 in FIG. 8(b). FIGS.1, 3 and 4 show the state that a part of the resin mold 360 is projectedfrom the upper end of the bobbin 15. The resin mold part 360 does notcontain a filler of iron oxide. The reason for applying the resin mold360 to the base part 360 is as follows. The bobbin 15 in the embodimenthas the insulation property but contains iron oxide. Thus the bobbin 15is not always complete in the point of the insulation property.Therefore among the base part 35 a, at least a part embedded in thebobbin 15 is coated with an insulation resin not including iron oxideand insulation of the terminal is assured.

The other terminals 36, 37 have an arm part binding one end of the coilonly at one side, although not shown. According to the reason as abovedescribed, in the terminals 36, 37, at least a part embedded in thebobbin is coated with an insulation resin mold 360.

As shown in FIG. 4, the bobbin 15 is wound by the valve opening coil 12and the holding coil 13, and the terminals 35, 36, 37 are arranged onthe upper end surface. Thus the coil module is constituted.

In the arm part of each terminal from the bobbin 15, respective coilends are bound and joined in fusing.

In FIGS. 1 and 3 numeral 23 designates a swirler pushing unit, numeral30 designates a flange for mounting the injector, numeral 31 designatesa collet, numeral 32 designates a filter, numeral 60 designates acorrugated packing, numeral 70 designates a removing part of theconnector 34 a, and numeral 71 designates a connector guide.

According to the embodiment, following effects are obtained.

(1) Heat resisting property of the bobbin 15 is improved, and moreoverthe heat radiating property for the coil heating is raised.

Accordingly even if the case of the electromagnetic coil having the coilcharacteristics where the environment temperature is violent and theheating temperature is high as in the direct injection, reliability ofthe coil and the bobbin is maintained and the long life of the injectioncan be assured.

(2) Even if two types of electromagnetic coils different incharacteristics are used, three terminals of the coil module are used.

Accordingly parts are used rationally and in intensive method, and thecoil module hence the injector is made compact and the cost reduction isintended.

(3) Also when the coil terminal 35 is drawn to the connector part 34 a,the consideration is done in a part of the terminal so as to avoid thecore 11. Accordingly the degree of freedom in the design of the terminallayout can be raised, and moreover three or more coil terminals arearranged on one connector in intensive method and the injector can bemade compact.

In the above-mentioned embodiment, although iron oxide is exemplified asa filler of good heat conductivity to be contained in the bobbin 15, thefiller of good heat conductivity is not limited to this, but otherwiseceramics with good heat conduction (for example, alumina), BN (boronnitride) or the like may be used. Such good heat conductive material maybe mixed in one type or two or more types.

Further connection of the valve opening coil 12 and the holding coil 13may be considered in various modes.

For example, as shown in FIG. 9, in the first terminal 36, one end ofthe valve opening coil 12 and one end of the holding coil 13 may beconnected to the plus side of the battery power source 53, and in thesecond terminal 35 other end of the valve opening coil 12 may beconnected to the first switching element 51 a, and in the third terminal37, other end of the holding coil 13 may be connected to the secondswitching element 52 a. In this case, the energizing control of the coilmay be similar to FIG. 7. Also in the embodiment, the connector of threeterminals can be realized in the injector having the valve opening coil12 and the holding coil 13.

Further in the injector having the valve opening coil 12 and the holdingcoil 13, if independent terminals 35 to 37 and 80 are prepared in eachcoil end, four-terminal structure as shown in FIG. 10 can be adopted.Also in this case, when the terminal base part is arranged at theopposite side of the connector part with respect to the axial line ofthe main body of the injector, curved parts 35′, 80′ are formed in apart of the terminal. Thus the degree of freedom of the terminal layoutand intensive use of plural terminals in one connector can be intended.

In the embodiment, the terminal 80 comprises the base part 80 a and thelead frame 80 b.

Industrial Applicability

According to the present invention as above described, the heatradiation property of the coil of the injector accompanied by theperformance improvement is raised, and the injector can withstand thehigh heat environment well, and the long life of the injector isassured, moreover the injector is made compact and the cost reductioncan be intended.

What is claimed is:
 1. A fuel injector having a valve driven by electromagnetic force, which injects fuel directly into a cylinder of an internal combustion engine, comprising: a first coil in which a large excitation current flows for a short time during a beginning of a valve opening operation so as to substantially secure magnetomotive force necessary to open said valve; a second coil in which a relatively small excitation current flows so as to substantially secure magnetomotive force to hold the valve in an open state after said valve is opened; and a bobbin on which said first and second coils are wound; wherein said bobbin with said first and second coils is formed by a resin molding material having a heat conductivity between 1.0-3.0 W/mk, and wherein said first and second coils are arranged on an axial direction of said bobbin, a flange for partitioning between said first coil and said second coil is provided at the bobbin, and said flange extends to the inner surface of a yoke housing the first and second coils.
 2. The fuel injector according to claim 1, wherein said bobbin is formed by a synthetic resin containing a filler having good heat conductivity.
 3. The fuel injector according to claim 1, further comprising a stationary core arranged at a center of a main body of the fuel injector, said first and second coils arranged at the outside of said stationary core through said bobbin; a cylindrical yoke arranged at the outside of said first and second coils; wherein said bobbin is formed by a synthetic resin containing a filler having good heat conductivity, and wherein heat of said first and second coils is conducted to said core and said yoke through said bobbin, and further an air gap is formed between the outside surface in said coil and an inner circumference of said yoke.
 4. The fuel injector according to claim 1, wherein said bobbin is formed of polyphenylene sulfide containing iron oxide and/or alumina as a filler.
 5. The fuel injector according to claim 1, wherein said bobbin is constituted by iron oxide and/or alumina in 30-80 weight %, and further by polyphenylene sulfide and glass fiber.
 6. The fuel injector according to claim 1, wherein said fuel injector is a battery-type injector driven by supplying a battery voltage to said first and second coils directly. 